Digital systems of data transmission are being used more and more in the transmission of signals because of the various advantages they provide. The analog signal representing the information to be transmitted is sampled and is quantized in amplitude. The continuous scale of the values presented by the signal is replaced by a sequence of discrete values which are normally coded in binary code. Thus, the analog signal to be transmitted is converted to a binary sequence which will not be appreciably affected by the length of the transmission path. Only a binary decision has to be taken by the signal repeaters provided along the transmission path and this makes their design and operation easier. Also, such digital processing of the signals permits a simple and economical application of the time multiplexing principle being used in the telephone networks. Finally, it enables the samples to be stored in a computer bulk memory from which they can be selectively fetched as required.
The major systems using digital signal quantization are based on pulse coded modulation (PCM), delta modulation, or differential pulse coded modulation (DPCM). In these systems, either the sample or the variation of the signal from one sample to the next is coded by rounding the value to be coded to the closest quantization level.
Whatever type of coding is in use, the quantization involves a difference between the coded signal and the original signal. This difference appears as a quantization noise which should be reduced to a minimum to obtain the best representation of the coded signal.
Various systems and methods for reducing this noise are known in the art.